As well known to those skilled in the art, a manifold absolute pressure (MAP) sensor is installed in a suction manifold of an internal combustion engine and is used for auxiliarily controlling suction timing of mixed gas into a cylinder by sensing the internal pressure of the cylinder and outputting a signal, indicative of the loaded condition of the engine, to an electronic control unit (ECU) for the engine. Such a MAP sensor thus allows the mixed gas to be appropriately fed into the cylinder in response to the operation of a fuel control valve and maintains a stable operation of the engine.
FIG. 3 is a sectional view showing the construction of a known MAP sensor for internal combustion engines. As shown in the drawing, the housing of the known MAP sensor is comprised of two parts, that is, a top case 20 and a bottom case 21 which are integrated into a single structure. The bottom case 21, having a pressure inlet port 22 on its bottom, is provided with a fitting groove on its top surface, thus being integrated with the top case 20, with the lower edge of the top case 20 being fitted into the groove 23. After the lower edge of the top case 20 is fitted into the groove 23, a thermosetting epoxy bond 24 is uniformly applied onto the junction between the two cases 20 and 21, thus fixing the top case 20 onto the bottom case 21. However, the epoxy bond 24 is applied onto the inside and outside of the junction between the two cases 20 and 21. In order to define a space for the epoxy bond 24 at the junction, the width of the fitting groove 23 is larger than the thickness of the lower edge of the top case 21, thus allowing the top case 20 to be moved on the bottom case 21 in the event of the bond 24 being not applied onto the junction. Therefore, the known MAP sensor may fail to be precisely assembled and it is very difficult to assemble the sensor, thus reducing productivity of the MAP sensors. The epoxy bond 24 is exposed to the outside of the housing, thus spoiling the appearance of the sensor. The integration of the two cases 20 and 21 is accomplished by applying the bond 24 onto the junction between the two cases 20 and 21 and the sensor housing regrettably has a structural limit with a low vibration resistance. Therefore, the known MAP sensor may fail to effectively resist an external impact and may be easily cracked due to such an impact.
The fitting groove 23 is formed on the top surface of the bottom case 21. Therefore, when a gap is unexpectedly formed in the bonding line at the junction between the top and bottom cases 20 and 21, it is possible to allow moisture or impurities to be introduced into the sensor housing through the gap. In addition, the epoxy bond 24, which is interiorly applied onto the junction, generates gas during a hot drying process for the bond 24 and allows the gas to remain in the housing. The above-mentioned moisture, impurities and gas may contaminate and break the parts in the sensor housing, thus causing an operational trouble of the sensor and reducing the operational precision of the sensor while sensing the pressure in a cylinder.
In the housing of the above sensor, both a sensor member 25 and a circuit board 26 fail to be stably supported because both the member 25 and the board 26 are supported only by a fitting force of the sensor member 25, which is fitted into the pressure inlet port 23 of the bottom case 21. Therefore, both the sensor member 25 and the circuit board 26 may be easily moved and cause a crack at the bonded junction of the housing in the event of external vibrations being applied onto the sensor.